Fuse construction



G. F. LAING FUSE CONSTRUCTION Filed April 14,' 1948 G do XNTOR. K

, 0f 7&1 dif?,

Patented Aug. 7, 1951 FUSE CONSTRUCTION Gordon F. Laing, Delavan, Wis.,assignor, by mesne assignments, to Economy Fuse and Manufacturing Co.,Chicago, Ill., a corporation of Illinois Application April 14, 1948,Serial No. 20,920

(Cl. 20o-123) 3 Claims.

The present invention relates to fuse construction.

More particularly, the present, invention relates to fuse constructiondesigned to open an electric circuit with a minimum formation of gasand/or flame under conditions approximating short circuit and which willhave a predeterminable time lag in the event of reasonable overload ofprolonged duration.

An object of the present invention is to provide a fuse construction ofthe kind referred to embodying a heat capacity member having relativelyhigh specific heat and high electrical conductivity for providing thedesired time lag.

A further object is to provide an electric fuse construction havingmeans for blowing under short circuit conditions with a minimum of gasand/or flame and having novel heat reservoir means for providing thedesired time lag under overload conditions. l

A further object is to provide an improved fuse construction havingmeans for open circuiting said fuse construction with a minimum of gasand/or flame under short circuit conditions and also having improvedmeans for controlling the open circuiting of said fuse constructionunder prolonged overload conditions.

A further object is to provide an improved fuse construction havingmeans adapted to blow with a minimum of gas and/or flame under shortcircuit conditions, Which means may be enclosed within an inert powder,said fuse construction having improved means for open circuiting with apredeterminable time lag under overload conditions, said fuseconstruction being provided with means for protecting said opencircuiting means from interference by said powder.

A further object is to provide a fuse construction having certainty ofaction, sturdiness, cheapness of manufacture, and which is well adaptedto meet the needs of` ordinary service.

Further objects will appear as the description proceeds.

Referring to the drawings- Figure l is a longitudinal sectional view ofa fuse embodying the principles lof the present invention;

Figure 2 is a sectional view taken along the plane indicated by thearrows 2-2 of Figure 1;

Figure 3 is a view in side elevation of the fuse elementI illustrated inFigures 1 and 2;

Figure 4 is a sectional view taken along the plane indicated by thearrows 4-4 of Figure 1; and

Figure 5 is a sectional view taken along the plane indicated by thearrows 5--5 of Figure 1.

The numeral I0 indicates a cylindrical casing within which is housed afuse element indicated as a whole by the numeral Il. Disposed at the twoends of the casing I8 are cap members l2-I2 of cup-shaped conformationadapted to be slipped over the ends of the casing I0 and to be securedto said casing. The bottoms of said cap members I2-I2 are apertured forthe reception of terminal blades or contact members I3, I3. United toeach of the terminal blades I3, I3 is a metal plate I3a adapted tocontact the adjacent end of the casing I0. Bottomed in said cap membersI2, I2 are washers I3b, I3b adapted to be held by said cap membersagainst the corresponding plates I3a, I3a. The washers I3b, I3b areprovided with slots closely fitting the blades I3, I3.

The fuse element I I is made up fundamentally of the following elements:a slug It of copper or other material having a relatively high specificheat and high electrical conductivity, providing a metallic heatreservoir member which slug will preferably be of cylindricalconformation and preferably will have projections or ends I5 and I6projecting from the two sides thereof; a pair of diaphragms Il, I1preferably of a slightly greater diameter than the diameter of the slugIl which daphragms are adapted to fit rather closely within thecylindrical casing I0; a fusible link I8 designed to fuse underconditions approximating a short circuit, which link should open circuitthe fuse construction under such conditions with a minimum of gas and/orllame, one end of said fusible link being thermally and electricallyconnected to the projection I5 of the slug Il, the other end of saidlink I8 being electrically connected to one terminal blade I3; theflexible strip 20 having one end soldered tolthe projection I6 of theslug I4 and having its other end soldered or otherwise connected to theother terminal blade I3; and a spring member 22 carried by that terminalblade I3 which is connected to the flexible member 20, insulated fromthe flexible member 20 but positioned to exert pressure upon saidflexible member 2li to urge it out of electrical contact with theprojection IG if and when the solder between said flexible member 20 andthe projection I6 should melt.

The fusible link I8 is illustrated as having a plurality of restrictedportions 23, 23 alternating with relatively wide portions 24, 24. Theend portion 25 of the fuse link I8 is adapted to be soldered to theprojection I5 of the slug I4 and for this purpose said projection I5 maybe provided with a flat surface whereby to facilitate the solderingoperation. The opposite end portion 26 of the link I8 is physically andelectrically united to a terminal blade I3.

The flexible strip 20, which may be composed of copper or otherelectrically conductive metal, has its extremity 21 physically andelectrically united to the right hand terminal blade I3. The otherextremity 28 of the flexible strip 20 is soldered t0 the projection IBof the slug I4. The solder which unites the extremity 28 of the flexiblestrip 20 with the projection I6 should have a lower melting point thanthe solder which is used to unite the fusible link I8 with itsprojection I5 and its terminal blade I3 and should have a lower meltingpoint than the solder which unites the extremity 21 of the fusible link20 with its terminal blade I3.

The spring member 22 may be made of beryllium copper or other resilientmaterial capable of retaining its spring properties un'ler thetemperatures expected to be encountered in the operation of the fuse.The extremity 29 of the spring 22 is physically united to thecorresponding terminal blade I3. The other extremity of the spring 22 isprovided with a coating 30 of ceramic cement or other insulatingmaterial to prevent the passage of electric current by way of the spring22 to the flexible member 20. Said spring 22 is adapted to exert forcethrough the non-conducting coating 30 against the extremity 28 of theflexible member to break contact between the flexible member 20 and theprojection I6 when the solder between the extremity 28 and theprojection I6 has melted.

The solder used to unite the extremity 28 of the flexible member 20 withthe projection I6 should be of eutectic composition, that is, acomposition having a low and definite melting point. For this purpose itis at present preferred to utilize an alloy consisting of:

Per cent Tin, approximately 50 Lead, approximately 32 Cadmium,approximately 18 Such a composition has a sharp melting point and willretain its holding properties substantially until completely melted.

It is preferred to have the fusible link I8 and the flexible strip 20 so'designed that upon the passage of electric current through the fuseassembly substantially the same amount of heat will be developed in theexible strip 20 as in the fusible link i8. In other words, said link I8and said exible member 20 are so correlated that passage of electriccurrent therethrough will develop the same amount of heat in each ofthem. This 'precaution will prevent variations which might otherwiseoccur if the fuse is reversed end for end when mounted in a Verticalposition,

The space between the left-hand diaphragm I'I and the left-hand plateI3a may be filled with an inert powder indicated by the numeral 3|. Thispowder is disposed in-enveloping relationship with the fusible link I8and will assist in quenching the arc formed when the fuse is subjectedto short circuit conditions. The diaphragms ITT-I1 serve to prevent thepowder 3| from interfering with the mechanical functioning of the spring22 and the flexible strip 20 when opening on overload.

Though a preferred embodiment of the present invention has beendescribed in detail, many modifications will occur to those skilled inthe art and it is intended to cover all such modications that fallwithin the scope of the appended claims;

'What is claimed is:

1. In a fuse element, in combination, a heat reservoir member having twoends and comprising a mass of metal of relatively high specic heat, afusible link having one of its extremities in electrical connection withone end of said reservoir member, a terminal contact member united tothe other extremity of said link, a movable metal member having one ofits extremities in connection, by means of solder, with said reservoirmember at the other end of said reservoir member, another terminalcontact member in electrical connection with the other extremity of saidmovable metal member, and a spring member biasing said movable metalmember out of contact with said reservoir member, insulating means forpreventing passage of electric current through said spring member, thesolder connecting said movable metal member to said reservoir memberbeing adapted to fuse before any other of said connections of said fuseelement upon the passage of electric current therethrough, said link andsaid movable metal member being s0 correlated that passage of electriccurrent in series therethrough will develop the same amount of heat ineach of them.

2. In a fuse element, in combination, a heat reservoir member having twoends and comprising a mass of metal, a fusible link in electricalconnection with one end of said reservoir member, a diaphragm located atone end of said reservoir member, said diaphragm being of cylindricalcontour adapted to fit Within an enclosing casing, a movable member ofelectrically conductive material, one end of said movable member beingin electrical connection with the other end of said reservoir member bymeans of a fusible solder, and a spring biasing said movable member outof engagement with said other end of said reservoir member, insulatingmeans for preventing passage of electric current through said spring,said solder being adapted to fuse before any other of said connectionsof said element upon the passage of electric current therethrough, saidlink and said movable member being so correlated that passage ofelectric current in series therethrough will de- -velop the same amountof heat in each of them.

3. In a fuse element, in combination, a heat reservoir member having twoends and comprising a mass of metal of relatively high specific heat, afusible link having one of its extremities connected by means of solderto one end of said reservoir member, a terminal contact member united'to the other extremity of said link, a movable metal member having oneof its extremities connected by means of solder to said reservoir memberat the other end of said reservoir member, another terminal contactmember electrically connected to the other extremity of said movablemetal member, and a spring member biasing said movable metal member outof contact with said reservoir member, insulating means for preventingpassage of electric current through said spring member, the solderconnecting said movable metal member to said reservoir member having alower melting point than the solder connecting said fusible link to saidreservoir member, said link and said movable metal member being socorrelated that passage of electric current in series therethrough willdevelop the same amount of heat in each of them.

GORDON F. LAING.

REFERENCES CITED The followingreferences are of record in the le of thispatent:

UNITED STATES PATENTS Date

